The Worker interface of the Web Workers API represents a background task that can be easily created and can send messages back to its creator. Creating a worker is as simple as calling the Worker() constructor and specifying a script to be run in the worker thread.

Workers may in turn spawn new workers as long as those workers are hosted within the same origin as the parent page. In addition workers may use XMLHttpRequest for network I/O, with the stipulation that the responseXML and channel attributes on XMLHttpRequest always return null.